looking for good shell programming books?

sorry, i deleted a recent email where someone was looking for a good intro to shell programming (emphasis: programming, not usage). my thoughts: first, one book that was mentioned was by ellie quigley. i remember a book by her on perl. awful, awful book. loaded with errors. personally, i wouldn't go near anything by her unless she's improved dramatically over the years. second: for maximum portability, consider sticking to strict POSIX constructs. yes, bash has lots of cool features. too many, in fact. if you're having to push the bounds of simple POSIX programming, you should probably be looking at another language. again, that's a personal opinion, but it's just too much of a pain to try to remember whether a particular shell language construct was bourne, korn, bash or some intersection thereof. third: good shell programming books? frankly, i haven't found any. and i'm still looking for one to use as a student text in a shell programming class. so far, i use my own manual and include the POSIX standards as a printed supplement. but i'd still like to find a decent book, ideally POSIX-oriented. rday